1. Field of the Invention
This invention relates to an optical information recording medium for use with the apparatus in the field of optical memory, and more particularly to a phase-changeable type optical information recording medium comprising a phase-changeable recording layer, capable of recording, reproducing, erasing and overwriting information by reversibly changing the phase of the recording layer with application of optical beams to the recording medium.
2. Discussion of Background
The so-called phase-changeable type recording media are conventionally known, in which information is recorded therein, reproduced therefrom and erased therefrom with application of electromagnetic waves, for example, a laser beam to the recording medium to change the phase of a recording layer of the recording medium, for example, from a crystalline state to an amorphous state or from one crystalline state to another crystalline state.
Intensive research and development activities concerning the above-mentioned phase-changeable type optical information recording media have been recently conducted because it is possible to overwrite information in the recording medium by the application of a single beam thereto, which is considered to be difficult with the magneto-optical memory technology, and an optical system for a drive unit for the optical information recording medium is comparatively simple in the mechanism.
As representative examples of such a phase-changeable type optical recording medium, there are disclosed in U.S. Pat. No. 3,530,441 recording media which comprise a recording layer comprising a chalcogen-type alloy such as Ge-Te, Ge-Te-Sb, Ge-Te-S, Ge-Se-S, Ge-Se-Sb, Ge-As-Se, In-Te, Se-Te or Se-As.
In addition, for the purpose of improving the stability and high-speed crystallization, an alloy in which Au is added to a Ge-Te based alloy is disclosed in Japanese Laid-Open Patent Application 61-219692, an alloy in which Sn and Au are added to the Ge-Te based alloy is disclosed in Japanese Laid-Open Patent Application 61-270190; and Pd is added thereto as disclosed in Japanese Laid-Open Patent Application 62-19490. Furthermore, to improve the repetition performance of the recording and erasing operation, a specific composition ratio of the Ge-Te-Se-Sb alloy is proposed for use in the recording layer of the recording medium as in Japanese Laid-Open Patent Application 62-73438.